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August 24, 2012

Methylation May Hold Key To Genetic Differences In Humans And Chimps

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April Flowers for redOrbit.com - Your Universe Online

Much has been made of the fact that ninety-six percent of a chimpanzee's genome is the same as a human's. However, it is that other four percent, and the vast differences, that pique the interest of Georgia Tech's Soojin Yi.

For example, why do humans have a high risk of cancer while chimps rarely develop the disease?

In a new study published in September's American Journal of Human Genetics, Yi looked at brain samples from each species. Differences in certain DNA modifications, called methylation, may contribute to phenotypic changes. The results of the study also hint that DNA methylation plays an important role for some disease-related phenotypes in humans, including cancer and autism.

“Our study indicates that certain human diseases may have evolutionary epigenetic origins,” says Yi, a faculty member in the School of Biology. “Such findings, in the long term, may help to develop better therapeutic targets or means for some human diseases. “

DNA methylation modifies gene expression but doesn't change a cell's genetic information. Yi and her team generated genome-wide methylation maps of the prefrontal cortex of multiple humans and chimps in an attempt to understand how the methylation differs between the two species.

Hundreds of genes were found that exhibit significantly lower levels of methylation in the human brain than in the chimp brain, most of them promoters involved with protein binding and cellular metabolic processes.

“This list of genes includes disproportionately high numbers of those related to diseases,” said Yi. “They are linked to autism, neural-tube defects and alcohol and other chemical dependencies. This suggests that methylation differences between the species might have significant functional consequences. They also might be linked to the evolution of our vulnerability to certain diseases, including cancer.”